Transfection of an inducible p16/CDKN2A construct mediates reversible growth inhibition and G1 arrest in the AtT20 pituitary tumor cell line

Recent studies have shown that methylation of the CpG island within the p16/CDKN2A gene is associated with an absence of p16 protein in human pituitary tumors. However, the effect of restoration of p16 protein expression in this tumor type has not been investigated. In the absence of an available human pituitary cell line we first assessed the suitability of the mouse corticotroph cell line AtT20 as a model system. Initial experiments showed that the p16/CDKN2A gene was not expressed, whereas a transcript for RB1 was detected as assessed by RT-PCR. Further studies showed the p16/CDKN2A gene to be homozygously deleted. The absence of p16/CDKN2A and presence of RB1, the down-stream effector of p16-mediated cell cycle arrest confirmed the suitability of the AtT20 cell line as a model system. Stable transfectants were generated in which p16/CDKN2A is regulated by an inducible promoter. The regulatory effects of p16/CDKN2A expression on cell proliferation were assessed and complemented by fluorescence-activated cell sorting (FACS) analysis of cell cycle profile. Induced expression of p16/CDKN2A resulted in a profound inhibition of cell growth and G1 arrest (80-82%). Western blot analysis showed concomitant expression of p16 protein in arrested cells and a shift in the phosphorylation status of pRB toward its hypophosphorylated form. To further confirm that expression of p16/CDKN2A mimicked its in vivo role, reversibility was assessed using alternate cycles in the presence and absence of inducer (isopropyl-1-thio-beta-D-galactopyranoside). Over three cycles the absence of induced expression of p16/CDKN2A resulted in release from G1 arrest. These results show that, in a pituitary cell line model, restoration of p16 expression is indeed sufficient to arrest cells in G1 and inhibit cell proliferation and is reversible. Thus restoration of p16 expression through novel strategies, including gene therapy or demethylating agents, may offer successful therapeutic intervention in human forms of this disease.

Surgical removal of an ependymoma from the third ventricle of a cat

A 10-year-old spayed domestic shorthaired cat was presented for behavioural changes, signs suggestive of visual deficits and aimless circling. Neuro-ophthalmological examination suggested the cat had central blindness. CT scans following administration of iohexol demonstrated a contrast-enhancing mass in the vicinity of the third ventricle resulting in obstructive hydrocephalus. Following rostral tentorial craniotomy and incision through the cerebral cortex, the third ventricle was approached via the dilated left lateral ventricle. An ependymoma was seen through a dorsocaudolateral incision into the third ventricle, and removed by gentle manipulation and suction. The cat recovered unremarkably, regaining normal vision and behaviour.

Analysis of cyclin D1 (CCND1) allelic imbalance and overexpression in sporadic human pituitary tumors

Cyclin D1 plays an important role in the regulation of cell progression through G1 of the cell cycle and has been demonstrated to have oncogenic properties. Using RFLP-PCR, an A/G polymorphism within the cyclin D1 (CCND1) gene was analyzed in 151 sporadic human pituitary tumors, of which 60 were informative at this locus. Further analysis showed that in 15 of 60 (25%) tumors, there was evidence of allelic imbalance, which is indicative of gene amplification. Allelic imbalance was observed more frequently in invasive tumors (11 of 29 tumors; 38%) than in their noninvasive counterparts (4 of 31 tumors; 13%; P = 0.02). Forty-six of the tumors informative for the polymorphism were available for immunohistochemical analysis. Cyclin D1 expression (nuclear and/or cytoplasmic) was detected in 25 of 46 (54%) tumors. Of these cases, expression of nuclear cyclin D1 was detected in 9 of 46 (20%) tumors, whereas 16 of 46 (35%) tumors showed cyclin D1 staining exclusively confined to the cytoplasm. Neither nuclear staining nor cytoplasmic staining was observed in any of the normal pituitaries or in the negative control. Expression of cyclin D1 was observed in significantly more nonfunctional tumors (18 of 27 tumors; 67%) than in somatotrophinomas (7 of 19 tumors; 37%; P = 0.046). Nuclear cyclin D1 expression was observed more frequently in nonfunctional tumors (8 of 27 tumors; 30%) than in somatotrophinomas (1 of 19 tumors; 5%; P = 0.04). There was no correlation between cyclin D1 expression and tumor grade or between allelic imbalance of CCND1 and cyclin D1 expression. We conclude that amplification of CCND1 occurs in pituitary tumors and that the overexpression of cyclin D1 may be an early event in tumorigenesis. Cyclin D1 overexpression occurring in the absence of CCND1 allelic imbalance suggests that additional mechanisms responsible for deregulated cyclin D1 expression are involved in human pituitary tumorigenesis.

Hypermethylation of the p16/CDKN2A/MTSI gene and loss of protein expression is associated with nonfunctional pituitary adenomas but not somatotrophinomas

The cyclin-dependent kinase inhibitor 2A/multiple tumor suppressor gene 1 (CDKN2A/MTS//p16) plays an important role in the control of progression from G to S-phase of the cell cycle through the inhibition of CDK4-mediated RBI phosphorylation. In this study we investigated 46 nonfunctional pituitary tumors and 21 somatotrophinomas for aberrant methylation of the CpG island contained within the CDKN2A gene as an alternative mechanism of gene silencing. We demonstrate methylation in 32/46 (70%) of nonfunctioning tumors, in contrast to 2/21 (9.5%) somatotrophinomas and 0/15 histologically normal postmortem pituitaries. Methylation in noninvasive and invasive nonfunctional tumors was approximately equal at 15/20 (75%) and 17/26 (65%), respectively. Immunohistochemical analysis showed an absence of CDKN2A protein in 25/32 (78%) methylated nonfunctioning tumors, demonstrating a highly significant overall correlation (P = 0.00007) between hypermethylation of the gene and absence of the p 16 protein. The association between hypermethylation and absence of CDKN2A protein remained when the cohort of nonfunctional tumors was further subdivided into noninvasive 12/15 (80%; P = 0.004) and invasive 13/17 (76%; P = 0.01), suggesting this to be an early event in pituitary tumorigenesis. In contrast, a single invasive methylated somatotrophinoma failed to express the CDKN2A protein. These data show that hypermethylation of the CpG island within exon 1, but not exon 2, of the CDKN2A gene is frequently associated with loss of protein expression in nonfunctional pituitary tumors, but not somatotrophinomas, suggesting different tumorigenic pathways.

Benign masses in the pericardium of two dogs

Two miniature Schnauzer dogs were treated for pericardial masses. In one dog the mass consisted of necrotic fat that was attached to the apex of the pericardium by a pedicle. No obvious communication with the abdomen was present. The second dog had a peritoneopericardial hernia associated with a chronic cystic haematoma. In each case the mass was presumed to have arisen following congenital displacement of the omentum into the pericardium. The pericardial mass was removed and subtotal pericardectomy performed in both dogs. Recovery was complete in each case.

Chromosome 13q deletion mapping in pituitary tumors: infrequent loss of the retinoblastoma susceptibility gene (RB1) locus despite loss of RB1 protein product in somatotrophinomas

Two recent studies have described allelic loss of an RB1 intragenic marker on chromosome 13q in aggressive and metastatic pituitary tumors that did not correlate with loss of pRB. The second report also showed that losses were more frequently associated with a more centromeric marker. Because both of these studies suggest the presence of another or other tumor suppressor genes (TSGs) on 13q, we carried out an allelotype analysis encompassing known and recently described TSG loci on 13q, together with immunohistochemical analysis of pRB. We analyzed 82 nonfunctional tumors and 53 somatotrophinomas subdivided into invasive and noninvasive cohorts. A significantly higher frequency of loss, at one or more of 13 markers, was evident in the invasive nonfunctional tumors (54%, 26 of 48) than in their noninvasive counterparts (29%, 10 of 34). An approximately equal frequency of loss was apparent in invasive (28%, 5 of 18) and noninvasive (31%, 11 of 35) somatotrophinomas at one or more markers. In those tumors harboring deletion, loss at two or more markers was more frequent in invasive nonfunctional tumors 65% (17 of 26) compared with 36% (4 of 11) of their noninvasive counterparts. In somatotrophinomas, 40% (2 of 5) of invasive tumors as compared with 64% (7 of 11) of noninvasive tumors had evidence of two or more deletions. In tumors showing loss at two or more loci, the majority showed large deletions; however, loss of the RB1 intragenic marker D13S153 was infrequent. In most cases, loss at individual markers was more frequent in invasive tumors than their noninvasive counterparts. A marker 3 cM telomeric to RB1 (D13S1319) showed the highest frequency of deletion in both invasive cohorts (29% of somatotrophinomas and 24% of nonfunctional tumors). Immunohistochemical analysis of pRB showed frequent loss in somatotrophinomas (27%, 9 of 33) in comparison with 4% (2 of 53) of non-functional tumors. Although loss of pRB did not correlate with loss of an intragenic marker or tumor grade, it was significantly associated with the somatotrophinoma subtype (P = 0.002). These data suggest that chromosome 13q is a frequent target for allelic deletion in pituitary tumors and point to another or other TSG loci in these regions.

Sequence analysis and transcript expression of the MEN1 gene in sporadic pituitary tumours

The majority of pituitary tumours are monoclonal in origin and arise sporadically or occasionally as part of multiple endocrine neoplasia type 1 (MEN1). Whilst a multi-step aetiology involving both oncogenes and tumour suppressor genes has been proposed for their development, the target(s) of these changes are less clearly defined. Both familial and sporadic pituitary tumours have been shown to harbour allelic deletion on 11q13, which is the location of the recently cloned MEN1 gene. We investigated 23 sporadic pituitary tumours previously shown to harbour allelic deletion on 11q13 with the marker PYGM centromeric and within 50 kb of the MEN1 locus. In addition, the use of intragenic polymorphisms in exon 9 and at D11S4946, and of telomeric loci at D11S4940 and D11S4936, revealed that five of 20 tumours had loss of heterozygosity (LOH) telomeric to the menin gene. However, the overall pattern of loss in informative cases was indicative of non-contiguous deletion that brackets the menin gene. Sequence analysis of all MEN1 coding exons and flanking intronic sequence, in tumours and matched patient leucocyte DNA, did not reveal mutation(s) in any of the 23 tumours studied. A benign polymorphism in exon 9 was encountered at the expected frequency, and in seven patients heterozygous for the polymorphism the tumour showed retention of both copies of the menin gene. Reverse transcription polymerase chain reaction analysis of ten evaluable tumours and four normal pituitaries revealed the presence of the menin transcript. Whilst these findings suggest that gene silencing is unlikely to be mechanistic in sporadic pituitary tumorigenesis, they do not exclude changes in the level or stability of the transcript or translation to mature protein. Our study would support and extend very recent reports of a limited role for mutations in the MEN1 gene in sporadic pituitary tumours. Alternatively, these findings may point to an, as yet, unidentified tumour suppressor gene in this region.

Substrate specificity of barley cysteine endoproteases EP-A and EP-B

The cysteine endoproteases (EP)-A and EP-B were purified from green barley (Hordeum vulgare L.) malt, and their identity was confirmed by N-terminal amino acid sequencing. EP-B cleavage sites in recombinant type-C hordein were determined by N-terminal amino acid sequencing of the cleavage products, and were used to design internally quenched, fluorogenic peptide substrates. Tetrapeptide substrates of the general formula 2-aminobenzoyl-P2-P1-P1'-P2'-tyrosine(NO2)-aspartic acid, in which cleavage occurs between P1 and P1', showed that the cysteine EPs preferred phenylalanine, leucine, or valine at P2. Arginine was preferred to glutamine at P1, whereas proline at P2, P1, or P1' greatly reduced substrate kinetic specificity. Enzyme cleavage of C hordein was mainly determined by the primary sequence at the cleavage site, because elongation of substrates, based on the C hordein sequence, did not make them more suitable substrates. Site-directed mutagenesis of C hordein, in which serine or proline replaced leucine, destroyed primary cleavage sites. EP-A and EP-B were both more active than papain, mostly because of their much lower Km values.

Changes in the levels of seven proteins involved in polypeptide folding and transport during endosperm development of two barley genotypes differing in storage protein localisation

The Russian barley cultivar Nevsky lacks gamma 3 hordein and accumulates most of its hordein in the lumen of the endoplasmic reticulum and only a minor portion in the vacuole. In wild type barley and all other temperate cereals, storage proteins are deposited in the vacuole. F1 crosses revealed that the Nevsky phenotype is recessive; but the extent of hordein accumulation in the endoplasmic reticulum in F2 endosperm lacking gamma 3 hordein was very much less than in the Nevsky parent. In order to study the Nevsky endosperm phenotype we have measured the levels of seven proteins and two mRNAs involved in protein folding in the ER lumen or ER to Golgi transport during endosperm development. The protein levels were unaltered in Nevsky as compared to the wild-type variety Bomi. When the levels of these seven proteins were correlated with the rate of hordein accumulation, four of these (HSP70, PDI, Sar1p and Sec18p) were consistently up-regulated with hordein synthesis. Accumulation of hordein in the endoplasmic reticulum appears to be determined by the absence of gamma 3 hordein, or the product of a gene closely linked to it, plus one or more other recessive genes.

Chromosome 9p deletions in invasive and noninvasive nonfunctional pituitary adenomas: the deleted region involves markers outside of the MTS1 and MTS2 genes

We have screened 57 cases of primary, nonfunctional, pituitary adenomas for loss of heterozygosity of markers on chromosome 9p. Using a panel of 11 microsatellite markers, we found hemizygous deletion with at least one of the markers in 18 tumors (31.5%). The frequency of loss was similar in both noninvasive (8 of 26; 31%) and invasive tumors (10 of 31; 32%), suggesting that loss on this chromosome might be an early event in pituitary tumorigenesis. Two discrete areas of loss were punctuated by a region of retention of heterozygosity between the markers D9S171 and IFNA, indicative of homozygous deletion. However, multiplex PCR analysis (MTS1 and MTS2) and the presence of a 3' untranslated region polymorphism in MTS1 suggested that neither of these tumor suppressor genes was homozygously deleted. In 6 of the 18 tumors showing LOH, sufficient DNA was also available for Southern blot analysis and, in all cases, showed retention of MTS1. Cell mixing experiments of tumor cell DNA homozygously deleted for MTS1 with DNA in which neither copy of the gene was deleted only gave rise to a signal at contamination levels greater than 30% and could discriminate homozygous and hemizygous loss. These studies support the recent findings that mechanisms other than hemi- and homozygous deletion are most likely responsible for the loss of MTS1 gene product in pituitary tumors (M. Woloschak et al., Cancer Res., 56: 2493-2486, 1996.). These data show that losses on either side of 9p21-22, both or either of which may be deleted, are involved in pituitary tumorigenesis and provide evidence for distinct suppressor gene loci, in addition to MTS1, on chromosome 9p.

Death by inmate--multiple murder in a maximum security prison

The authors report the killing of two inmates by a third inmate in a maximum security prison in the State of Wisconsin. All three had been sentenced to life imprisonment for murder, and one as a notorious serial killer. They touch on the variables of jail/prison overcrowding, the psycho-social traits and psychopathology of inmates, and their ethnicity as potential factors in violent crimes. They conclude that the selection of inmate housing should take into consideration the past history, the personality and the possible psychopathology of the inmate.

A role for gamma 3 hordein in the transport and targeting of prolamin polypeptides to the vacuole of developing barley endosperm

Hordein synthesis, transport and deposition was analysed by immunocytochemistry in developing endosperm cells of wild-type (Carlsberg II) and mutant varieties deficient in B hordein (hor2ca), gamma 1 hordein (Donetsky), gamma 2 hordein and minor B hordein polypeptides (Haisa), or gamma 3 hordein (Nevsky). In all varieties, hordein polypeptides were detected both in the cytoplasm as globules, ranging in diameter from 50 nm to 1.24 microns, and in the vacuole as protein bodies. In the cytoplasmic globules B and C hordein polypeptides are assembled as a core and are surrounded by an outer layer of gamma 1 and gamma 2 hordein. The globules apparently fuse several times in the cytoplasm before entering the vacuole. Absence of gamma 3 hordein in the mutant Nevsky leads to a dramatic change in hordein polypeptide targeting, the hordein storage proteins being largely deposited in the lumen of the rough endoplasmic reticulum. gamma 3 Hordein is unique among the sulphur-rich hordein polypeptides, being monomeric and forming only intramolecular disulphide bridges, while the other B and gamma hordein polypeptides are aggregated by intermolecular disulphide bridges. Retention of hordein in the rough endoplasmatic reticulum in the absence of gamma 3 hordein suggests that gamma 3 hordein may maintain the prolamin storage polypeptides in a transport competent state. The sequence of the mature gamma 3 hordein polypeptide was deduced from a cDNA clone, and compared with gamma 2 hordein. The epitope recognized by the gamma 1 + gamma 2 hordein-specific BX monoclonal antibody used for immunocytochemistry was mapped to include E190 and K193, by synthesizing overlapping oligopeptides.

The primary structure of a cDNA for PsaN, encoding an extrinsic lumenal polypeptide of barley photosystem I

A cDNA clone encoding a 15,501 Da photosystem I (PSI) subunit of barley was isolated using an oligonucleotide based on the NH2-terminal amino acid sequence of the isolated protein. The polypeptide, which migrates with an apparent molecular mass of 9.5 kDa on denaturing SDS-PAGE, has been designated PSI-N, and the corresponding gene is PsaN. Analysis of the deduced protein sequence indicates a mature protein of 85 amino acid residues and a molecular mass of 9818 Da. PSI-N is a hydrophilic, extrinsic protein with no predicted membrane-spanning regions. The transit peptide of 60 residues (5683 Da) contains a predicted hydrophobic alpha-helix, suggesting that the protein is routed into the thylakoid lumen. Thus, PSI-N is the second known lumenal protein component associated with PSI, together with PSI-F.

Hormone stimulated steroid biosynthesis in granulosa cells studied with a fluorogenic probe for cytochrome P-450SCC

The regulation of steroidogenesis by luteinizing hormone (LH) was studied in granulosa cells during follicular development using a fluorescent reporter assay based on the metabolism of a fluorescent probe specific for cytochrome P-450SCC (cholesterol side-chain cleavage enzyme). Intact granulosa cells or mitochondria were obtained from the first (F1) second (F2) and third (F3) largest preovulatory follicles of the hen ovary and incubated with the fluorogenic substrate. Metabolism of this substrate by cytochrome P-450SCC generates the highly fluorescent resorufin anion (the fluorescent reporter). In both mitochondria and intact granulosa cells, incubated with the fluorescent substrate, an increase in resorufin fluorescence was observed and the increase was greater in samples derived from F1 than in samples from F2 or F3. In cells, LH added simultaneously with the P-450SCC substrate significantly increased resorufin fluorescence above control values in a time- and dose-dependent manner up to 2-3 h after the incubation was initiated. Forskolin and 8-bromo-cAMP also stimulated metabolism of the P-450SCC substrate significantly by 15 min. When granulosa cells were preincubated with LH before exposure to the P-450SCC substrate resorufin fluorescence was significantly attenuated compared to controls (not exposed to LH in the preincubation period). The decrease in resorufin fluorescence observed when cells were pretreated with LH, may be due to the release of cholesterol from endogenous pools and its competition with the exogenous fluorogenic for the substrate P-450SCC enzyme. In granulosa cells that were preloaded with the P-450SCC substrate, the stimulatory effect of LH treatment remained constant from 30 min to 2 h after hormone addition. The results show that this fluorescent probe can be used in a rapid assay for the continuous measurement of the acute effects of hormone agonists on cholesterol conversion to pregnenolone in steroidogenic cells.

Flow cytometric analysis of steroidogenic organelles in differentiating granulosa cells

Functional and structural changes accompany the differentiation of granulosa cells during follicular development. We used flow cytometry and fluorescent dyes to characterize two organelles important to the steroidogenic process. Mitochondria, which contain the rate-limiting enzyme responsible for cholesterol conversion to pregnenolone, and lipid droplets, which store cholesterol substrate, were probed in viable hen granulosa cells during differentiation. The fluorescent dye Dio3-C5 (DiO) was used to probe mitochondrial membrane potential, indicative of mitochondrial activity and/or number, during rapid granulosa cell differentiation in a hierarchy of individual developing hen preovulatory follicles (F6, smallest, to F1, largest). Cellular DiO fluorescence, granularity, and cell size were significantly elevated with increasing maturation state. Treatment with LH significantly increased DiO fluorescence in granulosa cells from F1 but not F3. The increased mitochondrial activity/number in granulosa cells that accompanies follicular maturation and is influenced by LH may reflect, at least in part, increased activity or amount of hormone-regulated mitochondrial enzymes controlling steroidogenesis. Flow spectrofluorometry and the metachromatic lipid dye, nile red, were used to probe lipid droplets in differentiating granulosa cells from F6 to F1. There was a dramatic increase in the fluorescence component related to lipid droplets with increasing stages of follicular maturation, suggesting recruitment of lipids into droplets during the differentiation of granulosa cells into hormone-responsive steroidogenic cells. The results demonstrate the dynamic nature of the granulosa cell morphology involved in steroidogenesis during follicular development.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural and biochemical characterization of a Synechocystis 6803 mutant with inactivated psbA genes

A constructed Synechocystis 6803 mutant with a deletion of the three psbA genes was subjected to ultrastructural and biochemical characterization. This D1-depleted mutant also lacks the D2 protein and the chlorophyll a-binding protein CP-47. A general ultrastructural comparison between the wild type and the mutant did not reveal any major changes in cell appearance. We found by freeze-fracture analysis that approximately 60% of the endoplasmic face particles found in the wild-type thylakoids were missing in the mutant. A corresponding increase in protoplasmic face particles in the mutant thylakoids may represent a subcomplex of those photosystem II (PS II) polypeptides which accumulate in the absence of the D1 protein. Correlation of the PS I:PS II ratio with freeze-fracture data indicates that there is only one reaction center in each PS II freeze-fracture particle. Fluorescence measurements show that the CP-43 polypeptide in the mutant binds chlorophyll and that it may be connected to the phycobilisomes. Excitation energy can be transferred from the phycobilisomes to photosystem I in the absence of the photosystem II reaction center heterodimer and CP-47. This suggests that exciton transfer to photosystem I is mediated either directly by a terminal phycobilisome transmitter or via CP-43.

Identification of the photosystem I antenna polypeptides in barley. Isolation of three pigment-binding antenna complexes

The light-harvesting antenna of barley photosystem I (LHCI) was isolated from native photosystem I (PSI) complexes and fractionated into three pigment-protein subcomplexes using two consecutive rounds of green gel electrophoresis. Each complex showed a characteristic polypeptide composition and low-temperature fluorescence emission spectrum; they were designated as LHCI-730, LHCI-680A and LHCI-680B. Their four apoproteins of 21, 22, 23 and 25 kDa were purified and NH2-terminal sequences were determined; in the case of the NH2-terminally blocked 25-kDa protein, an internal sequence was obtained after cleavage with endoproteinase Lys-C. This made possible an assignment of the four proteins to the four types (I-IV) of genes coding for chlorophyll a/b proteins of PSI (cab or lha genes). The LHCI-730 complex was isolated as a heterodimer composed of the 21-kDa (LHCI type IV) and the 22-kDa (LHCI type I) polypeptides. Each LHCI-680 complex had a single apoprotein. LHCI-680A consisted of the 25-kDa (LHCI type III) and LHCI-680B of the 23-kDa (LHCI type II) polypeptides. LHCI-680B was associated with the non-pigmented PSI-E subunit, indicating that this protein may function in the binding of this antenna to the reaction centre.

On the Crystal Structure of Bi2Te4O11

Bi2Te4O11 is monoclinic, space group P21/n; the lattice parameters derived from a Guinier powder pattern ( Si standard) are: a = 6.9909(3), b = 7.9593(3), c = 18.8963(8) � , β = 95.176(3)�, Z = 4, V = 1047.15 �. The structure was solved independently from both single-crystal X-ray data and a combination of X-ray and neutron powder data. It is an anion-deficient superstructure of fluorite in which can be recognized the ordered intergrowth of fluorite-type Bi2Te2O7 and rutile-type Te2O4. Lone-pair electrons are stereochemically active.